1. 35.2 Defenses against Infection

2. Key Questions
At the end of this section you should be able to answer the following questions:
How does the skin work to prevent disease?
How does our body fight against disease causing bacteria and viruses?
How do the different immune cells fight disease?

3. Vocabulary Inflammatory Response Humoral immunity Histamine
Cell-mediated immunity
Interferon
Fever
Immune response
Antigen
antibody

4. Antigen vs. Pathogen Pathogen: A disease causing organism.
Examples: Viruses and Bacteria.
Antigen:
Any foreign substance that can trigger an immune response.
Examples: Viruses, Bacteria, Pet Dander, Pollen, etc.

5. Thinking Question:
The body’s defenses are divided up into two types, specific and non-specific, in your own words, state what you think each one does.

6. What are the body’s nonspecific defenses against infection?
Nonspecific defenses include the skin, tears, and other secretions, the inflammatory response, interferons, and fever.
Nonspecific: acts against a wide range of pathogens.

7. First Line of Defense Nonspecific defense Skin: Physical barrier
Tears, Saliva, and Mucus: contain lysozyme (enzyme that breaks down bacterial cell walls)
Protect eyes, mouth, and nose

8. Second Line of Defense Inflammatory Response, including histamines
Interferons
Fever

9. Inflammatory Response
Causes infected areas to become red and painful, or inflamed.
The response is initiated when mast cells release chemicals known as histamines.
Mast Cell: found in tissues throughout the body in close proximity to the surfaces of the body. They release histamines when stimulated by pathogens.

10. Inflammatory Response
Histamines: increase the flow of blood and fluids to the affected area. This allows white blood cells, including phagocytes, to move into tissues and destroy the invading bacteria.
Histamines: Organic Nitrogenous compound, helps white blood cells move from the capillaries into the infected tissues to attack pathogens.
Phagocytes: white blood cells that engulf and destroy bacteria.
Activity in the area makes that area feel warm.

11. Interferons
Interferons: proteins produced by some host cells to interfere with the creation of viral proteins.
Interferons buy time for the body’s specific defenses to respond and attack the viral infection.
Interferons are proteins that communicate to nearby cells preparing them to prevent viruses from dividing.

12. Fever
The immune system releases chemicals that signal the hypothalamus to increase body temperature.
Low fevers stimulate interferon production and speed up white blood cell growth.
Also slows the growth of some pathogens and speeds up the immune response in several ways

13. Specific Defenses: The Immune System
What is the function of the immune system’s specific defenses?

14. Specific Defenses: The Immune System
The immune system recognizes, attacks and remembers “others” that have invaded.
This recognition, response and memory are called the immune response

15. Specific Defenses: The Immune System
The Immune System’s specific defenses distinguish between “self” and “other,” and they inactivate or kill any foreign substance or cell that enters the body.

16. B and T Cells
B-cells and T-Cells are both produced in the bone marrow. However:
 B- Cells, mature in Red Bone Marrow
T – Cells mature in the Thymus Gland ( an
endocrine gland)

17. Antibodies
The immune system reacts to antigens by attacking the invader or producing cells that make antibodies
The main role of antibodies is to tag antigens for destruction

18. Antibody

19. The Immune System in Action
What are the body’s specific defenses against pathogens?
Two main styles:
Humoral immunity
Cell-mediated immunity

20. Humoral Immunity
Fights pathogens through antibodies that circulate in the blood and lymph
The response is activated when antibodies on B cells bind to antigens on a pathogen.
Antibodies have two antigen binding sites on the prongs of the “Y”
These bind to specific antigens

21. Cell Mediated Immunity
Produces Cytotoxic T Cells, Memory T Cells, and Helper T Cells
Helper T-Cells activate Humoral Immune Response
Cytotoxic T-cells destroy infected cells

22. Specific Immune Response

23. Vaccines
A weakened or killed pathogen is injected into a person so their specific defenses will make antibodies to recognize the pathogen.

24. Active and Passive Immunity
Active Immunity is acquired from having a disease or getting a vaccination. This is long term.
Example: Measles Vaccine
Passive immunity is acquired from another organism and tends to be short term
Example: From mother to baby through breast feeding